'Double upgraded' is the term that I have heard most call it. I will list some basics here that will satisfy most of your questions. I think that all crafted items are able to be double upgraded now, although I am not sure about some of the weapons. Feel free to ask me for help if you have any further questions and/or problems with crafting.
Any simple/martial and exotic weapons crafters out there that know exactly which weapons can't be double upgraded? Please post here and inform us.
- must be at least lvl 30, I recommend more since the xp cost can delevel you to below 30
- must have the required gold and xp amount on your pc
- either have in your inventory or craft a master artisan item, then use a master artisan crafting station and an extra choice will appear near the bottom of the menu *upgrade item*
- choose upgrade,place item in the crafting station,a script will appear and tell you a cost of 100k gold & 2.5k xp,agree to this and the item will be single upgraded and placed back in your inventory
- repeat this process to double upgrade the item, your cost will be an additional 135k gold & 5k xp
- single upgrades increase the ability, skills, saves and in some cases the ac by +1, double upgrades increase the item by another +1
- pc's must be level 25 to wear single upgraded items, lvl 30 for double upgraded items
- an item can be single upgraded, and at a later time taken back to be double upgraded
- do not put upgraded items in the Avendell Anvil